The present invention relates to nuclear fuels, and more particularly to a fuel permitting the design of small, efficient reactors suitable for remote and mobile applications.
The relatively long fuel recycling times of nuclear reactors makes them well suited as power sources in mobile units, such as ships, submarines and satellites, and in remote locations, such as the Arctic, Antarctic, deep sea bases and outer space. For example, the exploration of the deep sea bed will require ample power sources sustainable without frequent refueling.
Mobile and remote applications place a premium on reactor compactness and fuel efficiency. Volume and mass constraints in satellite and submarine design, for example, dictate the use of lightweight and compact reactors. The inconvenience of refueling such mobile units makes high fuel efficiency desirable. Fuel efficiency is also desirable from the standpoint of conservation of natural reserves of fissile materials. Similar considerations govern the design of reactors for remote locations. The cost of transporting reactors and fuel to the Arctic or a deep sea drilling facility stresses the need for small, efficient reactors.
The TRIGA reactors, developed by General Atomic Company, include a variety of small, efficient reactors. The TRIGA reactors utilize metal hydride fuels, such as U-Zr-H. These fuels may include a fine dispersion of uranium fuel throughout a zirconium hydride matrix. The zirconium hydride matrix serves as a neutron moderator as well as a matrix for the fissile fuel. The metal hydride fuels are characterized by a large prompt negative temperature coefficient of reactivity, which provides for a high degree of inherent safety. Additional safety and durability are provided because U-Zr-H does not generally react with materials employed as coolants or structural members.
There are, however, some significant limitations to the metal hydride fuels heretofore developed. For one thing, at high temperatures hydrogen dissociates from the hydride. In the case of Zr-H, the hydrogen pressure is 1 atm. at 760.degree. C. This limits the operating temperature and the moderating ability of the metal hydride. The loss of hydrogen from the fuel matrix can also reduce the moderating efficiency of the hydride. A related problem concerns the atomic percent of hydrogen within the Zr-H matrix. Normally, Zr-H includes approximately 1.7 hydrogen atoms per zirconium atom (ZrH.sub.1.7). Finally, the zirconium itself does not contribute in any significant positive sense to the neutronic performance of an incorporating reactor.
It is an object of the present invention to provide an improved metal hydride fuel that can be used alone or in combination with other fuels. More particularly, the present invention is directed to a fuel with improved neutronics performance, improved moderating characteristics, and an enhanced large prompt negative temperature coefficient of reactivity. It is also an object of the present invention to provide a fuel which permits the design of improved small and efficient reactors.